FIG. 21 is a conceptual drawing illustrating a storage system using a library apparatus as a storage apparatus. In a general storage system, a host (host computer) 1 is directly connected to a real library apparatus 2. Accordingly, the host 1 controls a transfer mechanism 3 to mount/unmount physical volumes 4 onto/from physical drives 5. The host 1 then reads/writes data from/into the physical volumes 4 mounted on the physical drives 5.
FIG. 22 is a conceptual drawing illustrating a storage system using a virtual library apparatus 11. The virtual library apparatus 11 is disposed between a host 10 and a real library apparatus 12 and provides logical drives 13 and logical volumes 14 to the host 10. The real library apparatus 12 is, for example, a tape library apparatus, and each of physical volumes 17 is assigned with, for example, each tape housed in tape cartridge. The logical drives 13 are, for example, a cache disk 16, and each of the logical volumes 14 is assigned with, for example, each of a plurality of recording regions of the cache disk 16.
Although the host 10 is directly connected to the virtual library apparatus 11, the host 10 may treat the real library apparatus 12 as equivalent to the real library apparatus directly connected to the host 10. Accordingly, as in the storage system illustrated in FIG. 21, the host 10 is able to access the logical volumes 14 via the logical drives 13 within the virtual library apparatus 11 without being aware of the presence of the virtual library apparatus 11.
A controller 15 provided for the virtual library apparatus 11 stores data (logical volume data) to be recorded on recording regions of the cache disk 16 corresponding to the logical volumes 14. The cache disk 16 is disposed within the virtual library apparatus 11. Then, the controller 15 transfers data from the cache disk 16 to the physical drives 18 disposed within the real library apparatus 12 by performing migration processing asynchronously with access from the host 10.
The logical volume data stored in tapes corresponding to the physical volumes 17 within the real library apparatus 12 are transferred to the cache disk 16 and are stored therein as far as the storage capacity of the cache disk 16 permits. Accordingly, in response to a request from the host 10 to access the same logical volume 14 once again as that storing the data before, it is possible to promptly return a ready state response.
In contrast, if there is a shortage of the storage capacity of the cache disk 16, the controller 15 drives out the logical volume data stored in the cache disk 16 and transfers the driven data to a tape corresponding to a physical volume 17, by performing migration processing. This is performed on the basis of logic by considering, for example, the frequency of the usage of the logical volumes 14. With this operation, the storage capacity of the cache disk 16 for storing other logical volume data may be reserved in the cache disk 16.
The logical volume data driven out of the cache disk 16 of the virtual library apparatus 11 is transferred to the real library apparatus 12 by migration processing. Then, the real library apparatus 12 controls a transport mechanism 19 and a physical drive 18 to write the logical volume data into a tape corresponding to a physical volume 17.
If there is a request from the host 10 to mount the logical volume data on a logical drive 13, the logical volume data is read from the tape. Then, the read logical volume data is stored in recording regions of the cache disk 16 corresponding to the logical volumes 14 (RECALL processing). To complete such RECALL processing, it takes several tens of seconds to several minutes from a time at which the host 10 makes a request to mount the logical volume data until a time at which the mounting operation is finished.
FIG. 23A through FIG. 23C are conceptual drawings illustrating the state in which logical volume data is written in a recording region of a cache disk corresponding to a logical volume. A description is given below, assuming that a tape library apparatus is used as a backend by way of example.
In the virtual library apparatus 11, tape drives do not exist. However, from a viewpoint of the host 10, it appears as if there were tape drives in the virtual library apparatus 11. Thus, access from the host 10 to the logical drives 13 is the same as that to tape drives.
In a tape drive, data may be written into a tape while the tape is being transferred, which implements the sequential writing of data, thereby achieving fast access. However, because of the structure of media (tape), it is not possible to partially overwrite data stored in the tape.
FIG. 23A illustrates logical volume data stored in a recording region of a cache disk corresponding to a logical volume. Updating of the logical volume data having block ID 1 through block ID 3 stored in a recording region 941 may be performed by either of the incremental (additional) write system or the overwrite system.
In the incremental write system illustrated in FIG. 23B, additional new logical volume data 4 and 5 are written into a recording region 942 positioned after the recording region 941 in which the logical volume data 1 through 3 are stored. In the overwrite system illustrated in FIG. 23C, overwriting of data is started from the head (data having block ID 1) of the logical volume, and the entirety of the data including updated data, i.e., the updated logical volume data having block ID 1 through block ID 3, which is a series of the data reflecting the updated content, is written into a recording region 943.
FIG. 24A and FIG. 24B are conceptual drawings illustrating the state in which data is written in a tape corresponding to a physical volume. In updating processing on stored data, because of the structure of a tape, as described above, partial overwriting of data stored in the tape is not possible. Accordingly, the conceptual drawings of the physical volume illustrated in FIG. 24A and FIG. 24B are different from those of the logical volume illustrated in FIG. 23B and FIG. 23C.
More specifically, in the incremental write system, as illustrated in FIG. 24A, after a recording region 950 in which logical volume data having block ID 1 through block ID 3 are stored, updated logical volume data including the stored logical volume data having block ID 1 through block ID 3 and additional data having block ID 4 and block ID 5 is written into a recording region 951. Accordingly, in the incremental write system, the same data having block ID 1 through block ID 3 are recorded on the tape plural times, which demands an extra storage capacity.
In the overwrite system, as illustrated in FIG. 24B, updated logical volume data having block ID 1 through block ID 3 are written into a recording region 953 positioned after a recording region 952 in which existing logical volume data having block ID 1 through block ID 3 are already stored. Accordingly, in the overwrite system, the entirety of the logical volume data reflecting the updated content is written in the state in which the existing data remains in the physical volume, which also demands an extra storage capacity.
The following are reference documents.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2005-190139
[Patent Document 2] Japanese Laid-open Patent Publication No. 2005-122611